This invention relates to a dry type developing device for a copying apparatus or like apparatus, and more particularly it is concerned with a dry type developing device for developing a copy sheet on which an electrostatic latent image is formed by means of a magnetic brush, which device is provided with means for ensuring proper contact of the copy sheet with the magnetic brush so as to prevent soiling of the underside of the copy sheet or partial under-developing or non-developing of the electrostatic latent image.
The magnetic brush developing method is a dry type electrophotographic developing method which consists in supplying a magnetic developing agent to a magnetic brush forming roller which may be a magnetic roller or a non-magnetic roller having magnets built therein so as to form a magnetic brush, and rubbing the surface of the copy sheet supporting an electrostatic latent image thereon by the magnetic brush to supply toner particles to the electrostatic latent image to develop and render the same visible.
When this developing method is employed, an electrophotosensitive sheet, electrostatic recording sheet or other sheet (hereinafter referred to as a copy sheet) is fed to the magnetic brush and brought into contact therewith. It has hitherto been customary to supply the copy sheet directly to the magnetic brush, so that the manner in which the copy sheet is brought into contact with the magnetic brush may vary depending on the firmness of the sheet. When the copy sheet lacks firmness, the copy sheet is not brought into contact with the magnetic brush along the full width of the sheet and some regions of the latent image may remain non- or under-developed, so that there occur irregularities in the density of the toner image. When the copy is too firm, the leading end invades the layer of toner particles and moves therethrough and some toner particles move to the underside of the copy sheet, with the result that the underside of the copy sheet is soiled.
To remove the toner particles adhering to the underside of the copy sheet and soiling the same, it has hitherto been customary to employ a pump or magnet to draw off the toner particles by suction. This is disadvantageous in that the developing device becomes complex in construction and high in cost.